Tsushima Black Nagura

These black Nagura were quarried some time ago at a now
closed underwater mine on Tsushima Island off the coast of Nagasaki. Traditional woodworkers in
western countries referred to this stone as ‘Ocean Blue’, and they used these
stones for finishing the polishing stage on chisels and other fine cutters.
Allegedly, there is another type of Tsushima Black that was quarried inland at
another source. I am not certain whether
or not that the other type, referred to as ‘Mountain Tsushima’ is the same type
of stone. I have read and been told that it is not as fine or consistent as the
‘Ocean’ type.

These particular Nagura are in fact of the ‘Ocean’ variety.
They’re quite hard and the slurry they produce starts off being fine, but it
seems to break down considerably. Finishing a straight razor on Tsushima Black
slurry can be compared to finishing on Mejiro or Koma and possibly some Tomo
Nagura also.

The sides of each of these Nagura are sealed with cashew
lacquer, which is a traditional protective treatment. I am unable to tell if there
is a layer of rice paper under the lacquer but I suspect that might be the
case.

I’ve used these with great success mixed into a full Mikawa
Nagura progression, or as an option for touching up a slightly dull edge. They
are also ideal for raising a slurry on a full-size Tsushima Black bench-stone
Tennen Toishi.

Like most Nagura, they can be used on natural stones, as well as synthetics.

Thre’s a not-so-short clip showing Tsushima Black Nagura being used with a Naniwa ‘Snow White’ here.